1. Field of the Invention
The present invention relates to the linear dicarbonylation of difunctionalized butenes.
By "linear dicarbonylation" is intended the predominant formation of 3-hexene-1,6-dioic acid and/or the dialkyl esters thereof, by reacting carbon monoxide, if appropriate also an alcohol, with at least one butene disubstituted by hydroxyl, alkoxy or acyloxy radicals.
2. Description of the Prior Art
It is known to this art that diesters of 3-hexene-1,6-dioic acid can be hydrogenated into the corresponding diesters of adipic acid, which in turn can be hydrolyzed to produce adipic acid.
3-Hexene-1,6-dioic acid can itself be hydrogenated into adipic acid.
Adipic acid, one of the raw materials for producing nylon 66, is currently synthesized in vast amounts. For this fact alone, any novel process for the preparation of this diacid and/or derivative thereof is of basic interest.
European Patent Application EP-A-0,347,340 (corresponding to U.S. Pat. No. 4,925,973) describes a catalytic process for the preparation of diesters of 3-hexene-1,6-dioic acid by reacting carbon monoxide and an alcohol with at least one butene disubstituted by acyloxy radicals. Such linear dicarbonylation is carried out in the presence of a catalyst based on palladium and on a quaternary onium halide of a Group VB element selected from between nitrogen and phosphorus, said element being tetracoordinated to carbon atoms, with the proviso that the nitrogen may be coordinated to two pentavalent phosphorus atoms, and the halide anion being selected from between the chloride and bromide. Such a process permits conducting the carbonylation under conditions of pressure and temperature which are acceptable on an industrial scale, with an appreciable selectivity for a linear dicarbonylated final product, and wherein the proportions of monocarbonylated product and of branched dicarbonylated compounds are very small.
European Patent Application EP-A-0,395,545 describes a catalytic process for the preparation of 1,6-hexenedioic acid by reacting carbon monoxide and water with at least one butene disubstituted by acyloxy radicals. The linear dicarbonylation is also carried out in the presence of a catalyst based on palladium and on a quaternary onium chloride as indicated above.
Example 8 of this application, carried out using metallic palladium deposited onto charcoal and in the presence of tetrabutylphosphonium chloride, does not provide completely satisfactory results.
European Patent Application EP-A-0,395,546 describes, in particular, a process for the preparation of 3-hexene-1,6-dioic acid by reacting carbon monoxide with 2-butene-1,4-diol and/or 1-butene-3,4-diol.
The linear dicarbonylation is carried out in the presence of a catalyst based on palladium and on a quaternary onium chloride, also as indicated above.
Example 21 of this application, carried out using metallic palladium deposited onto charcoal in the presence of tetrabutylphosphonium chloride, also does not provide completely satisfactory results.
European Patent Applications Nos. 90/322,256, 90/322,257 and 90/322,258 respectively describe replacing the onium halide as defined above, at least partially, by a pair or couple constituted by certain inorganic halides and by a basic aprotic polar solvent.
French Patent Application No. 90/12,042 describes another catalytic process for the preparation of diesters of 3-hexene-1,6-dioic acid by reacting carbon monoxide with a 1,2-dialkoxy-3-butene, either alone or in admixture with a 1,4-dialkoxy-2-butene.
The linear dicarbonylation is carried out in the presence of a catalyst based on palladium and on an ionic chloride in which the cation is selected from among the alkali metal cations, alkaline earth metal cations and quaternary onium cations as defined above.
However, each of the aforedescribed catalytic processes for the linear dicarbonylation of difunctionalized butenes, the fundamental benefits of which are not in dispute, presents at least one of the following disadvantages and drawbacks:
(1) Certain sources of palladium, and in particular metallic palladium deposited on a support, do not exhibit a fully satisfactory activity under certain reaction conditions;
(2) The catalyst system exhibits an insufficient stability with time, manifested by the precipitation of palladium over time on the walls and base of the carbonylation reactor.
Thus, need continues to exist in this art for a catalytic process for the linear dicarbonylation of difunctionalized butenes, in which the palladium-based catalyst system exhibits improved stability and, if appropriate, improved catalyst activity.